1. Field of the Invention
The present invention relates to an improved catalyst for use in the ammoxidation of an unsaturated hydrocarbon to the corresponding unsaturated nitrile. In particular, the present invention is directed to the process for making an improved catalyst for the ammoxidation of propylene and/or isobutylene to acrylonitrile and/or methacrylonitrile, respectively. More specifically, the invention relates to the process for producing an improved multi-component ammoxidation catalyst wherein a portion of the catalyst comprising a complex of bismuth, molybdenum, cerium and at least one of sodium, potassium, cesium, rubidium, calcium, lanthanum or yttrium is preformed prior to combining with the remaining elements of the catalyst.
2. Description of the Prior Art
Catalysts containing oxides of iron, bismuth and molybdenum, promoted with suitable elements, have long been used for the conversion of propylene and/or isobutylene at elevated temperatures in the presence of ammonia and oxygen (usually in the form of air) to manufacture acrylonitrile and/or methacrylonitrile. In particular, Great Britain Patent 1436475; U.S. Pat. Nos. 4,766,232; 4,377,534; 4,040,978; 4,168,246; 5,223,469 and 4,863,891 are each directed to bismuth-molybdenum-iron catalysts which may be promoted with the Group II elements to produce acrylonitrile. In addition, U.S. Pat. Nos. 5,093,299, 5,212,137, 5,658,842 and 5,834,394 are directed to bismuth-molybdenum promoted catalysts exhibiting high yields to acrylonitrile.
In part, the instant invention relates to the preparation of bismuth-molybdenum-iron catalysts. Typically, such catalysts are produced in a batch process by simply combining and reacting, source compounds for the various metal components. However, more complex and multiple-step preparations have been used. For example, U.S. Pat. No. 4,040,978 taught a process for catalyst preparation where molybdates of each metal were separately made and then combined and reacted; and U.S. Pat. No. 4,148,757 taught a process for catalyst preparation where bismuth and molybdenum were first reacted to form a bismuth molybdate and then the bismuth molybdate was combined with a mixture of source compounds for the various other metal components.